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Comment by ssl-3 | Hacker News Reader

The presentation is nice, but some of the conversions are questionable.

For instance: The cost section, wherein 1kWh in the US is figured as having a cost of 9.7 cents.

In reality, it's not that way at all. Unless we're fortunate enough to live in an area where we can walk over to the neighborhood generating station and carry home buckets of freshly-baked electricity to use at home, then we must also pay for delivery.

On average, in 2025, electricity was 17.3 cents per kiloWatt-hour -- delivered -- for residential customers in the US.

https://www.eia.gov/electricity/monthly/epm_table_grapher.ph...

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I looked at the electric car example for the United States. It has 3 kilowatt hours priced at $0.51, 17 cents per kilowatt hour, which seems about right. The "petrol car" example at the top of the chart isn't powered by electricity so its cost number is not directly comparable to the things that consume electricity.

On the energy tab: It says that driving a petrol car 10 miles uses 10,000 Watt-hours, eg 10 kWh.

On the costs tab, for the United States: It says that this has a cost of $0.97.

97 cents ÷ 10kWh = 9.7 cents per kWh

(I didn't look further than that. Perhaps I should have.)

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edit: I now see a note at the very bottom stating that it is using an assumed "$0.17 for electricity".

$0.17 per kWh is plenty close enough for rough figurin', so I'd like to take this opportunity to retract my previous complaint.

Yes, for the petrol car it's showing primary energy from petrol (gasoline).

https://en.wikipedia.org/wiki/Gasoline_gallon_equivalent#Gas...

Assuming 33.41 kWh/gallon it takes about 0.3 gallons to get 10 kWh, which costs $0.97 at a pump price of $3.23 per gallon.

The electric shower also seemed pretty optimistic. I live in an area with about 50°F/10°C ground temperature and my 14.4 kW water heater can just keep a relatively efficient shower head flowing at a comfortable temperature.

Heat pump or resistive?

This one is resistive (tiny and cheap to purchase) but will be just an emergency-backup shower once my home renovations are done.

The house is getting a split-system air-to-water heat pump with an indirect tank for domestic hot water, so it should cut that down substantially (the unit maxes out at around 3kW input but likely will run longer to recover/preheat).

I had this problem once with a water heater: Get in shower, and things are nice and hot. But the temperature decreased rapidly, and immediately.

It turned out that it had been plumbed backwards.

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